Selective inhibition of exoplasmic membrane fusion in echinoderm gametes with jaspisin, a novel antihatching substance isolated from a marine sponge.

A specific inhibitor of fertilization of the sea urchin Hemicentrotus pulcherrimus was isolated from the extract of the marine sponge, Jaspis species. Chemical and spectral data of the purified substance, which was designated jaspisin, showed that it is a novel substance with the structure of sodium (E)-5,6-dihydroxystyryl sulfate. Jaspisin at 15 micrograms/ml inhibited exoplasmic fusion of the plasma membrane of acrosome-reacted sperm with the plasma membrane of the egg; it did not affect either the acrosome reaction in sperm or the egg cortical reaction, both of which involve endoplasmic membrane fusion events. When a fertilized egg was cultured in jaspisin, the embryo developed through the mesenchymal blastula stage. However, it was unable to hatch from the fertilization envelope, and spiculogenesis, in which cell-cell fusion of primary mesenchyme cells is involved, was prevented. Jaspisin at 8.6 micrograms/ml inhibited half the activity of hatching enzyme, a kind of Zn(2+)-dependent metalloendoproteinases. Because Zn(2+)-activated metalloendoproteinases are suggested to be involved in both sperm-egg fusion and fusion of primary mesenchyme cells (Lennarz, W.J., and Strittmatter, W.J. (1991) Biochim. Biophys. Acta 1071, 149-158), one of the possible explanations of the jaspisin effects is that the sulfate inhibits these cellular events through blockage of Zn(2+)-activated metalloendoproteinases that are involved in membrane fusion processes.